European freezers, and refrigerators with a freezer compartment, have a four star rating system to grade freezers. One star, [∗] : min temperature = −6 °C (21 °F). Maximum storage time for (pre-frozen) food is 1 week. Four star, [∗∗∗∗] : min temperature = −18 °C (0 °F). Maximum storage time for pre-frozen or frozen-from-fresh food is between 3 and 12 months. only a four star freezer is intended for freezing fresh food, and may include a "fast freeze" function (runs the compressor continually, down to as low as −26 °C (−15 °F)) to facilitate this. Three (or fewer) stars are used for frozen food compartments that are only suitable for storing frozen food; introducing fresh food into such a compartment is likely to result in unacceptable temperature rises.